Project Summary: This proposal aims to understand mental health professionals'concepts of mental disorders in light of (1) the current DSM and (2) a proposal for its revision. First, the DSM-IV purposely does not specify the causes of mental disorders because they are still controversial. Previous studies supported by NIMH, however, found that clinicians have rich causal theories about mental disorders and these theories determine which symptoms matter more in diagnoses. The proposed studies build on these studies and will further examine what moderates clinicians'use of their causal theories in diagnoses. In particular, Ahn, et al. (2006) found that clinicians only view some DSM mental disorders as kinds discovered in nature;others were thought of as culturally invented kinds. This proposal tests the hypothesis that the more clinicians believe that mental disorders are natural kinds, the more they will use their causal theories in categorization. These studies will use clinicians'categorization of mental disorders to illuminate a general cognitive mechanism by which causal knowledge influences categorization. Second, one prominent proposal for the next version of the DSM is to eliminate categories of personality disorders and to use only underlying traits. Existing cognitive theories of concepts and expertise predict that eliminating categories and imposing trait-based reasoning on clinicians would disrupt communicability of, memory for, and inferences about patients. However, dimensional systems might have great clinical utility if clinicians feel that the current taxonomy is incomplete or invalid. The proposed studies provide necessary in-depth tests of the clinical utility of the dimensional systems, which can inform decisions about their adoption. In sum, the proposal describes translational research: basic theories and methods developed in cognitive science are to be applied to understanding current clinical practices and the clinical utility of current and proposed taxonomy of mental disorders. Relevance to Public Health: Many Americans suffer from mental disorders and seek therapies from mental health practitioners. Yet clinicians'concepts of mental disorders are poorly understood, and the current taxonomy of mental disorders is controversial. The proposed studies will aid in understanding and improving clinical practices and in developing psychologically intuitive taxonomies of mental disorders in time for the next version of the DSM due in 2011.